Model-Based Electric Motor Testing

Saving time with the Parameter Identification method

Many modern electric motors are subject to 100% inspection following manufacture. The reasons for this are, on the one hand, that the motor is installed in an inaccessible location, inside a vehicle, for example, and on the other hand, because the end consumer expects total reliability. The costs of dismounting and re-installing a motor often exceeds the actual cost of the motor itself. For this reason it makes sense to perform total motor diagnostics following manufacture in order to find any latent production errors, as well as to ascertain the technical specs.

100% inspection by conventional test station methods is unfeasible for reasons of time, cost, and technical complexity. So a PI test station is the preferable choice.

This new technique of evaluating motors is based on pre-existing knowledge of the motor’s structure. This knowledge base is expressed in the form of differential equations describing the motor’s mechanical and electrical properties. Non-linear relationships are also taken into account. In the PI procedure, the motor voltage represents the input quantity and the motor current the output quantity of the modeling differential equation. Both quantities are easily measured directly. The unknowns are the coefficients (parameters), such as the motor resistance, friction constants etc., which are combined with the measured variables in an equation.

The tasks which PI testing performs is to find the set of parameters which best explains the measured variables on the basis of the specified model. This means that the system adjusts the model parameters in response to the difference between the output variables as predicted by the model and as actually indicated for the test object.